[meteorite-list] Orbital debris watching radar

[Matson, Robert]

Hi Darren,

> So, not really a coherent question but more of a musing-- just
> how small an object at what distance can the radars that constantly
> track orbital space program junk around the Earth reliably track?

A ballpark figure is ~10 cm diameter for low-earth-orbit objects
out to perhaps 800-1000 km.  However, I doubt a similar-sized meteoroid
would provide as strong a radar return due to the lack of metal
and/or artificial (flat) surfaces.  Still, I should think you could
pick up a basketball-sized stony meteorite in LEO.  Scale the radar
cross section by range^4 for higher altitudes (i.e. the diameter by
range^2).  For instance, if you can detect a 25-cm diameter object
at 1000-km range, then the object would have to be over 300 meters
in diameter to provide the same return at geosynchronous distance.
(Clearly such an object would show up in optical surveys like a
sore thumb; radar would only out-detect optical at LEO ranges.)

> And would there be any way to determine if a piece of orbiting
> debris was junk or an incoming lunar?

Yes -- continued tracking would provide a measure of the object's
drag coefficient.  The mass-to-area ratio would be quite high for
rocky material compared to that of most manmade space junk.  --Rob